The present invention relates to the doors for walk-in type freezers of the type having a barrier of flexible strips of plastic on the inner side of the doorway and, in particular, to an improved method of preventing the build up of ice along the frame of the door to insure the proper sealing of the door against the frame.
Walk-in type freezers are typically constructed on a concrete slab and have an insulating barrier in the concrete floor surrounding the perimeter of the freezer to prevent heat from the surrounding structure being conducted through the concrete floor to the interior of the freezer. The ceiling and the walls are formed from four inch thick panels having a central slab of insulating foam sandwiched between two metal plates. The interior of the freezer is accessible through a rectangular door cut in one of the walls. The door is typically six feet, eight inches high and three feet or six feet in width. The six foot wide door allows access to the interior of the freezer with a fork lift truck.
The door which closes against the opening in the wall is either hinged or is slideable on a track. If the door is hinged, it may have a central protrusion on the inner surface thereof which extends approximately two inches into the doorway such that when the door is closed, the protrusion occupies the outer 2xe2x80x3 of the 4xe2x80x3 wide column of space extending from the threshold to the top of the door frame.
The doors may be frequently opened and closed and are sometimes left open for extended periods of time while personnel transfer goods into or out of the freezer, or work within the interior of the freezer. To retain the cold air within the freezer while the door is open, a thermal barrier consisting of a plurality of strips of flexible material, such as plastic, are suspended above the door frame. The strips of flexible material may be transparent so that one entering or exiting a freezer can see any activity or obstructions on the opposite side of the doorway before passing through the thermal barrier. The barrier is preferably made of very light material, so that it does not form an obstruction to one passing through the doorway to enter or exit the freezer.
The freezers may also have an elevated insulated floor, and the same type panels which are used to form the walls of the freezer are laid horizontally to construct the insulated floor. The insulated floor, therefore, consists of a 4xe2x80x3 thick layer of foam with upper and lower sheet metal surfaces. A tongue formed from one of the insulating panels forming the floor extends across the threshold of the door such that a 4xe2x80x3 step up is required to enter the freezer door with the step up occurring parallel to the freezer""s outer wall.
Such walk-in type freezers tend to accumulate ice build up around the door frame and on the flexible thermal barrier caused by moisture suspended in the warm air from outside the freezer cooling and precipitating as it contacts cold surfaces and finally freezing when it is hit by the cold air from within the freezer. Over a period of time, a layer of ice will accumulate within the doorway, on the thermal barrier and on the outer surface of the wall surrounding the doorway which will obstruct the closing of the door. Ice build up will also reduce the effectiveness of the seal between the door and the wall allowing heat to enter the freezer, thereby reducing its efficiency. Ice also builds up on the threshold of the door and can be a hazard because it is slippery.
It would be desirable, therefore, to provide an improved method and apparatus for preventing the build up of ice around the perimeter of freezer doorway to thereby reduce or eliminate the obstruction caused by ice.
Briefly, the present invention is a method and apparatus for preventing the build up of ice on the perimeter of a freezer doorway where the freezer has a floor, a door frame and a door moveable from an open position to a closed position. The freezer also has a flexible thermal barrier suspended from the inner wall over the doorway. Regardless of how the door is mounted, when the door is in the closed position there is a column of air between the inner surfaces of the door and the thermo barrier bounded by the sides of the door frame, the threshold, and the upper surface of the door frame.
In accordance with the present invention, a heating element is positioned on or below the threshold of the doorway for heating the air in the column between the inner surface of the door and the thermal barrier. The heating element is continuously operated, regardless of whether the door is open or closed. When the door is closed, the heating element heats the column of air between the inner surface of the door and the thermal barrier to maintain the surfaces of the door frame and the thermal barrier at a temperature that is above the freezing temperature of water. When the door is open, the heated air moves upward along the outer surface of the thermal barrier to prevent cold air from within the freezer from freezing moisture accumulating on the door frame. The invention is useable for the doors of freezers regardless of whether or not the freezer is provided with an elevated, insulated floor.